Satellite inspection radar

ABSTRACT

A radar system allowing an inspecting satellite to approach another satellite within a number of feet without contact therebetween. The radar system utilizes a pair of wide-beam antennas located along the roll and pitch axes of the inspecting satellite. A short pulse radar associated therewith is used to obtain range to the closest point and a comparison is made between the range measurements of each antenna in a pair. Thus a type of &#39;&#39;&#39;&#39;sampled comparison&#39;&#39;&#39;&#39; system is provided at a PRF/4 rate.

United States Patent 1 Gaheen SATELLITE INSPECTION RADAR Inventor:Alfred F. Gaheen, Glen Burnie, Md.

Assignee: The United States of America as represented by the Secretaryof the Air Force, Washington, DC.

Filed: June 14, 1967 Appl. No.: 646,797

U.S. Cl. 343/13 R, 343/100 ST, 343/12 R, 343/13 R, 343/7 PF, 343/112 CA,244/1 SA Int. Cl. G01s 9/06 Field of Search 343/12, 13, 100 ST, 343/12R, 13 R, 112 CA, 7 PF; 244/1 SA, 1 SD References Cited UNlTED STATESPATENTS 9/1970 Morse 343/7 PF 1 Dec. 25, 1973 3,112,480 11/1963 Lakatos343/112 CA Primary Examiner-Samuel Feinberg Assistant ExaminerS. C.Buczinski Attorney-Harry A. Herbert, Jr. and George Fine [57] ABSTRACT 3Claims, 3 Drawing Figures areal] wa /Paw: Fa -reap A a I f r" 3 Eggamaze nwwmn k-lwwamx Q -fi y 7W3? l-fleEff fuws/ecssr 7 /6 n/P-rwtwins/mm:

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PATENTED UECZ 5 I973 SHEET 10F 2 INVENTOR. il EAWFZWIIEAM? SATELLITEINSPECTION RADAR The present invention relates to a radar systemassociated with a reconnaissance satellite to permit the reconnaissancesatellite to approach a target satellite without contact therebetween,and more particularly, a reconnaissance satellite equipped with a radarsystem employing a pair of wide-beam antennas located along the roll andpitch axes for comparison of range measurements derived therethrough.

The present invention provides a radar system which will allow closureof one satellite to within a number of feet ofanother and allow thefirst satellite to control its attitude with respect to the second suchthat no contact takes place between the two. The system would also be ofvalue to a non-cooperative rendezvous scheme where it is desired toutilize a number of other shortrange inspecting sensors on the targetsatellite.

Thebasic operating technique is to utilize a pair of wide-beam antennas(for example, isotropic) located along the roll and pitch axes of theinspecting vehicle. A short pulse radar is used to obtain the range tothe closest point and a comparison is made between the rangemeasurements of each antenna in a pair. Thus a type of sampled rangecomparison system is developed which is similar to amplitude or phasecomparison monopulse, but is sampled at a PRF/4rate.

The object of the present invention is to provide a radar system for areconnaissance satellite wherein the radar system employs a pair ofwide-beam antennas located along the roll and pitch axes of thesatellite for comparison of range measurements derived therethrough.

Another object of the present invention is to provide a radar system fora reconnaissance satellite wherein a pair of antennas associated withthe radar is located along the roll and pitch axes of the satellite anda comparison is made between the range measurements of eachantenna in apair.

Yet another object of the present invention is to provide a radar systemfor an inspecting satellite wherein the output of the radar system willbe range to the nearest point on a target satellite and a measurementbetween the roll and pitch axes of the inspector satellite and theclosest point in the target.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,however, its advantages and specific objects obtained with its use,reference should be had to the accompanying drawings and descriptivematter in which is illustrated and described a preferred embodiment ofthe invention.

FlG. 1 shows a preferred embodiment of the present invention in the formof a radar system for an inspecting (reconnaissance) satellite;

FIG. 2 shows the positioning on the inspecting satel lite of two pair ofantennas associated with the radar system of FIG. 1; and

FIG. 3 illustrates a time representation of a gating logic associatedwith the radar system of FIG. 1.

Now referring in detail to FIG. 1, there are shown two pair of wide-beamantennas. The wide-beam antennas may be, for example, isotropic. Thefirst pair consists of antennas l and 2, and the second pair of antennas.3 and 4. Antennas 1, 2, 3, and 4 are located along the roll and pitchaxis of inspecting satellite 50 shown in FIG. 2. A short pulse radarassociated with aforesaid antennas is utilized to obtain range to theclosest point of the satellite being inspected. Comparison is then madebetween the range measurements of each antenna in a pair. Thus a type ofsampled range compari son system is provided which is similar toamplitude or phase comparison monopulse, but is sampled at a PRF/4 rate.The following description of the systems operation will better bring outsome of the salient operating characteristics.

The transmitter section which is comprised of modulator l2 andtransmitter 13 is capable of generating a 10 nanosecond pulse with risetimes of 0.5 to 1 ns. PRF generator provides a pulse T(o) to modulatorl2. Modulator is connected to transmitter 13. The pulse from transmittergoes by way of duplexer to one of four antennas l, 2, 3 and 4 fortransmission depending on the position of diode switches 5, 6 and 7.Diode switches 5, 6 and 7 are controlled by the outputs of gates 8 and9, which are gated by flip-flop l0 and pass a pre T(o) pulse provided byPRF generator 11. The pre T(o) pulse occurs approximately 0.1 usecbefore the T(o) pulse. This allowance for switching time will cause theuseful PRF to be lower than the maximum value obtained for unambiguousrange measurement but it is not significant.

A time representation of gates 8 and 9 logic is shown in FIG. 2. A T(o)pulse from PRF generator 11 triggers flip-flop 10, the condition ofwhich allows passage of the following pre T(o) pulse through either gate8 or gate 9. The logic will switch every alternate two transmissions. Inthis manner transmission toward the satellite being inspected will bethrough antennas l and 2 successively and then antennas 3 and 4successively. Monitor 28 determines the state of switch 5 which in turndetermines which pair of antennas is being used and thus which axis isreferenced. Monitor 28 may be an oscilloscope. By allowing a lOQ tsswitching time, practical diode switches for handling signals of 10 kwpeak may be used.

The transmitter pulse is also fed to detector 15 and then used totrigger flip-flop l6. Flip-flop l6 feeds gate 18 which also receivespulses from clock 17. This allows passage of 500 me clock pulses intoconventional up-down counter 19.

The received pulse returned from the satellite being inspected followsthe same paths as the transmitted pulse as far as antennas 1-4 and diodeswitches 5-7 are concerned, but in the opposite direction. The receivedpulse then goes by way of duplexer 14 to diode switch 20. Diode switch20 also receives a pre T(o) pulse from PRF generator 11. The receivedpulse from diode switch 20 is fed to mixer 21. Mixer 2! is alsoconnected to local oscillator 33. The received pulse is thussuperheterodyned to an intermediate frequency. It is then fed throughamplifier 22 and detector 23. The detected pulse resets flip-flop 16,thereby preventing the entrance of any further pulses into up-downcounter 19. The output of the reset side of flip-flop 16 is passedthrough differentiator 24 and delay 25 and used to trigger flip-flop 26,which supplies the Add" and Subtract commands to up-down counter 19 insuch manner that the commands alternate at the PRF and the commandchange occurs just after the received pulse.

In the event that a pulse is not received, the pre T(o) pulse will resetflip-flop 26 and the count for that particular pair of transmissions iserroneous and would have to be rejected by the conventional attitudecontrol section 27.

By monitoring the position of diode switch 20, it is known which pair ofantennas is being used. The output of gate 8 is also used as a Readpulse for gates 29-32 to gate the counter information into the attitudecontrol section. This count will actually be the difference between therange measurements of either antennas 1 and 2, or 3 and 4. The state ofthe most significant digit will determine whether it is negative orpositive and thus provide a sense. The output gate 1 is delayed slightlyby delay 34 and used to reset up-down counter 19 to all os during the100 ns switching time.

Diode switch 20 was added to give more isolation between the transmitterand receiver crystals associated with duplexer 14. This switch must becapable of handling powers which are 20 db down from the transmittedpower and thus is a low level device. Switching time is 1 ns. It isswitched by the pre T(o) pulse and may also be switched (if desired) bythe lagging edge of the transmitted pulse. A signal of this type may beavailable in modulator 12.

The information content of the systems output will then be range to thenearest point on the target (satellite being inspected) and ameasurement between the roll and pitch axes of the inspecting satelliteand the closest point on the target. The net result of the entire systemwill be to cause the inspecting satellite to align its roll and pitchaxes parallel to the targets nearest point. Thus various inspectors willbe brought to bear on the target and collision should not take placeunless planned. It is to be noted that the components of the system areconventional and may be off the shelf units. However, it is the newcombination of these conventional components which provide a new result.

Obviously many modifications and valuations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise as described.

What is claimed is:

l. A radar mounted in an inspector satellite for observing a targetsatellite comprising means for generating pulses of short duration to bedirected towards said target satellite to provide return pulsestherefrom, a first, second, third and fourth antenna associated withsaid pulse generating means with said first and second antennas being afirst pair and said third and fourth antennas being a second pair,saidfirst pair being located along the roll axes and said second pairalong the pitch axes of said inspector satellite, switching means totransmit and receive said generated and said return pulses,respectively, by way of said first and second antenna successively andthen by said third and fourth antenna successively, means to measurefrom said return echoes the difference between the range measurements ofsaid first and second antenna from said target satellite and also thedifference between the range measurements of said third and fourthantenna from said target satellite.

2. A radar mounted in an inspector satellite for observing a targetsatellite as described in claim 1 further including means to monitorsaid first and second pair of antennas to determine the operative pair.

3. A radar mounted in an inspector satellite for observing a targetsatellite as described in claim 1 further including means to measurefrom said return pulses the closest range from said inspector satelliteto said target satellite.

1. A radar mounted in an inspector satellite for observing a targetsatellite comprising means for generating pulses of short duration to bedirected towards said target satellite to provide return pulsestherefrom, a first, second, third and fourth antenna associated withsaid pulse generating means with said first and second antennas being afirst pair and said third and fourth antennas being a second pair, saidfirst pair being located along the roll axes and said second pair alongthe pitch axes of said inspector satellite, switching means to transmitand receive said generated and said return pulses, respectively, by wayof said first and second antenna successively and then by said third andfourth antenna successively, means to measure from said return echoesthe difference between the range measurements of said first and secondantenna from said target satellite and also the difference between therange measurements of said third and fourth antenna from said targetsatellite.
 2. A radar mounted in an inspector satellite for observing atarget satellite as described in claim 1 further including means tomonitor said first and second pair of antennas to determine theoperative pair.
 3. A radar mounted in an inspector satellite forobserving a target satellite as described in claim 1 further includingmeans to measure from said return pulses the closest range from saidinspector satellite to said target satellite.